[codec] remove uses of fmt::format, move to absl::StrCat (#8801)
[codec] remove uses of fmt::format, move to absl::StrCat (#8801)

Removes the dependency on `fmt::format` in H1 codec. Eliminates the use of `fmt::format` to format HTTP requests. Instead uses `absl::StrCat`, which can handle hex values with `absl::Hex`. 

Signed-off-by: Asra Ali <da4828c05ee1cc5a64445440d12151dedd1ac4a8@google.com>
envoyproxy/envoy-wasm,jrajahalme/envoy,lyft/envoy,lizan/envoy,envoyproxy/envoy-wasm,istio/envoy,jrajahalme/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,eklitzke/envoy,istio/envoy,eklitzke/envoy,eklitzke/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,jrajahalme/envoy,lyft/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,lyft/envoy,jrajahalme/envoy,lyft/envoy,eklitzke/envoy,eklitzke/envoy,jrajahalme/envoy,envoyproxy/envoy-wasm,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,istio/envoy,istio/envoy,envoyproxy/envoy,lizan/envoy,istio/envoy,envoyproxy/envoy,lyft/envoy,lyft/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy,eklitzke/envoy,lizan/envoy,istio/envoy